The present claimed invention relates to a light irradiating unit, more specifically to a light irradiating unit that is preferably used to inspect an appearance or a flaw of a product by irradiating light in a factory or the like.
Conventionally, a halogen lamp is used as a light source for this kind of a light irradiating unit. Considering an efficiency or an accuracy in product inspection, however, the halogen lamp as a light source is not suitable to get enough stability in luminous intensity, life duration and a quick responsive characteristics. A plurality of LEDs are used as a new light source to solve this problem. More specifically, generally known is like a light irradiating unit that the present claimed inventor has invented and shown in Japan Patent Laid Open No. 2000-21206 in which a plurality of LEDs are arranged on a print substrate and light is introduced by the plurality of LEDs through a bunch of optical fibers or a plurality of LEDs are arranged on a concave face of a cone shape and light irradiated from the LEDs is directly focused. The reason why a plurality of LEDs are used is based on a fact that it is difficult for an LED in an elementary substance to obtain enough light volume.
Recently a light emitting element referred to as a power LED that can produce big light volume in an elementary substance has been developed. This power LED can flow electric current of several hundred mA and can produce light volume corresponding to the electric current unlike a conventional LED that can flow electric current of several dozen mA at most.
The above-mentioned power LED makes it possible to downsize a light source, thereby to provide a new usage and a new possibility.
With the power LED, however, heat dissipation is indispensable because of a heat problem due to a huge electric current. LEDs generally have low light volume and short life duration at a high temperature. Conventionally in a case wherein a plurality of LEDs are used, each LEDs is mounted on a substrate, which is also to simplify a process of fixing the LEDs, and big electric current does not flow each LEDs in an elementary substance and each LED is arranged separately. Then the heat problem can be solved by mounting the substrate on a housing having heat dissipating fins. The power LED has dissipated heat through a substrate made of aluminum, however, there is a limit to dissipate heat generated from a bare chip of the power LED because the aluminum substrate dissipates heat through a glass epoxy layer (heat conductivity 0.3˜0.4 W/mk) that is arranged for insulation. As a result, just adopting the power LED will increase the heat dissipating portion in size, which fails to downsize the light source.
Further, since there is also a limit to position the power LED accurately in mounting the power LED on the substrate with soldering, a positioning relationship of the substrate and the power LED is not uniform even though the substrate is mounted on the housing with positioning accurately. As a result, for example, it might fail to introduce light from the power LED into a light introducing end portion of an optical fiber accurately, thereby to generate a loss in light volume at the light introducing end portion and to loose benefit of the above-mentioned big light volume. In order to prevent this with a simple arrangement, time and a cost to assemble the light source might increase.
In order to solve all of the above problems, the present claimed invention mainly intends to provide a light irradiating unit wherein a power LED is used as a light source so as to contribute to a characteristics of heat dissipation, downsizing, simplifying an assembling process and an accuracy of illuminating light.